When video signals are to be read from a tape by a rotating video head in magnetic recording-reproduction systems (hereinafter referred to as "VTRs"), the tape must be caused to travel at a specified speed while being tensioned suitably.
In the following description, the expression "forward travel (drive) of the tape" means the transport of the tape from the supply reel side toward the take-up reel side via the head cylinder, and the expression "reverse travel (drive) of the tape" refers to the transport of the tape in a direction opposite to the forward direction, i.e., from the take-up reel side toward the supply reel side via the head cylinder.
Further the application of a brake to the supply reel support does not mean to stop the supply reel support by the brake but to apply a light braking action to the support to hold the tape tensioned.
Usually, the tape is caused to travel by rotating the reel support on the tape take-up side by the capstan motor, which therefore generally serves also as the motor for the reel support.
The tape as held between the capstan and a pinch roller has the speed of its travel controlled by the rotation of the pinch roller.
Further when the tape is caused to travel forward, it is practice to lightly brake the supply reel support by a brake band 41 (see FIG. 8) to hold the tape tensioned during the travel.
To cause the tape to travel reversely, the tape take-up rotation transmitting system is changed over for the supply reel support 12 to thereby drive the supply reel support.
If the brake is acting on the supply reel support at this time, a great rotational torque is required for driving the supply reel support. As shown in FIG. 8, therefore, brake release means has been proposed which comprises a brake release lever 42 having attached thereto one end of the brake band 41 and rotatable clockwise by the rightward movement of a control plate 2 through a lever 49 to release the supply reel support 12 from the brake band (Examined Japanese Utility Model Publication SHO 61-25080).
When the tape T traveling forward is to be driven reversely upon a change of mode, the supply reel support is temporarily rendered free for a period of time required for a change-over of the mechanical rotational system by a known swing idler mechanism, permitting a back tension lever 31 to withdraw the tape from the supply reel undesirably. This poses a serious problem in the case of VTRs having the edition function of accurately and quickly searching the frames for the desired image for reproduction or accurately setting the tape at the recording start point and end point.
Further with the conventional device shown in FIG. 8, the brake is actuated or released by moving the brake release lever 42 counterclockwise or clockwise through the sliding movement of the control plate 2. Accordingly, if the plate 2 is slidingly moved leftward after the tape has been driven reversely with the brake in a released state, the brake acts on the supply reel support 12 abruptly, giving rise to a trouble such as displacement or slackening of the tape.